<!doctype html>
<html>
<head>
<meta charset="utf-8">
<title>js简单验证码使用</title>
<style>
    .code
    {
         font-family:Arial;
         font-style:italic;
         color:blue;
         font-size:30px;
         border:0;
         padding:2px 3px;
         letter-spacing:3px;
         font-weight:bolder;            
         float:left;           
         cursor:pointer;
         width:150px;
         height:50px;
         line-height:60px;
         text-align:center;
         vertical-align:middle;
         background-color:#D8B7E3;
     }
     span {
        text-decoration:none;
        font-size:12px;
        color:#288bc4;
        padding-left:10px;
    }
 
    span:hover {
        text-decoration:underline;
        cursor:pointer;
    }
   
</style>
</head>
<script>
    //页面加载时，生成随机验证码
    window.onload=function(){
     createCode(4);    
    }
 
    //生成验证码的方法
    function createCode(length) {
        var code = "";
        var codeLength = parseInt(length); //验证码的长度
        var checkCode = document.getElementById("checkCode");
        var codeChars = new Array(0, 1, 2, 3, 4, 5, 6, 7, 8, 9,
        'a','b','c','d','e','f','g','h','i','j','k','l','m','n','o','p','q','r','s','t','u','v','w','x','y','z',
        'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z'); 
        //循环组成验证码的字符串
        for (var i = 0; i < codeLength; i++)
        {
            var charNum = Math.floor(Math.random() * 62);
            code += codeChars[charNum];
        }
        if (checkCode)
        {
            checkCode.className = "code";
            checkCode.innerHTML = code;
        }
    }
    
    //检查验证码是否正确
    function validateCode()
    {
        var checkCode = document.getElementById("checkCode").innerHTML;
        var inputCode = document.getElementById("inputCode").value;
        console.log(checkCode);
        console.log(inputCode);
        if (inputCode.length <= 0)
        {
            alert("请输入验证码！");
        }
        else if (inputCode.toUpperCase() != checkCode.toUpperCase())
        {
            alert("验证码输入有误！");
            createCode(4);
        }
        else
        {
            alert("验证码正确！");
        }       
    }    
</script>
<body>
    <div>
    <table border="0" cellspacing="5" cellpadding="5" >
        <tr>
            <td> <div id="checkCode" class="code"  onclick="createCode(4)" ></div></td>
            <td> <span onclick="createCode(4)">看不清换一张</span></td>
        </tr>
        <tr>
            <td>验证码：</td>
            <td><input type="text" id="inputCode"  style="float:left;" /></td>
        </tr>
        <tr>
            <td></td>
            <td><input type="button" onclick="validateCode()"  value="确定" /></td>
        </tr>
    </table>
    </div>
</body>
</html>